The acromags are on the UPS. I suspect the transient came in on one of the signal lines. Chub tells me he unplugged one of the signal cables from the chassis around the time things died on Monday, although we couldn't reproduce the problem doing that again today.
In this situation it wasn't the software that died, but the acromag units themselves. I have an idea to detect future occurrences using a "blinker" signal. One acromag outputs a periodic signal which is directly sensed by another acromag. The can be implemented as another polling condition enforced by the interlock code.
If the acromags lock up whenever there is an electrical spike, shouldn't we have them on UPS to smooth out these ripples? And wasn't the idea to have some handshake/watchdog system to avoid silently dying computers?
The problem encountered with the vac controls was indeed resolved via the recommendation I posted yesterday. The Acromags had gone into a protective state (likely caused by an electrical transient in one of the signals)